Field of the Invention
The present invention relates to a polishing end point detecting device for a wafer polishing apparatus, specifically to a polishing end point detecting device for a wafer polishing apparatus which polishes the wafer by Chemical Mechanical Polishing (CMP).
Description of Related Art
The CMP is often used in a manufacturing process of large scale integrated circuits (LSI) in order to polish an insulator film or a metal film. In this process, an accurate determination of a polishing end point is required.
One conventional example of the CMP is Japanese Patent Application Publication No.2000-186918, which discloses a method in which light is applied onto a polishing face of the wafer and a spectrum intensity distribution of the light reflected on the polishing face is measured whereby a polishing end point is detected. Another example is Japanese Patent Application Publication No.2000-183001 disclosing a method in which light is applied onto the polishing face of the wafer and a color component of the light reflected on the polishing face is detected whereby the polishing end point is detected. Still another example is a method in which light of a single wavelength is applied onto the wafer, and the polishing end point is detected by referring to variations of an intensity of the reflected light.
Japanese Patent Application Publication No.2000-186918 discloses a method in which a lens makes the light from a light source parallel light, that is applied onto the polishing face of the wafer, and only zero degree light (regular reflection light) reflected on the polishing face is selected out by a light shielding slit, then the spectrum intensity distribution of the separated light is measured. After that the measured spectrum intensity distribution is fitted with spectrum characteristics that have been stored beforehand; thereby the polishing end point is detected.
On the other hand, Japanese Patent Application Publication No.2000-183001 discloses a polishing end point detecting method in which light from the light source is conducted to the polishing face by the light guide so as to illuminate the polishing face, and the light reflected on the polishing face is then conducted into a color identification sensor by the light guide, whereby a color component of the reflected light is detected. Then, the detected color component is fitted with a reference color component that has been stored beforehand, whereby the polishing end point is detected.
However, the polishing end point detecting method of Japanese Patent Application Publication No.2000-186918 has a problem in that it requires the light for illuminating the polishing face to be strictly parallel light for which an optical adjustment is difficult. Moreover, since the regular reflection light forms an image at the outside of the light shielding slit by a slight inclination of a reflection surface or an aberration of a condenser optical system, an amount of the regular reflection light is reduced that passes through the narrow light shielding slit and thus an intensity of the light to be used for detecting is lowered, resulting in poor sensitivity. Further, the polishing end point detecting method also requires an illumination/light receiving optical system which uses a beam splitter for splitting applied light and reflected light, hence the light is not used efficiently.
The polishing end point detecting method disclosed in Japanese Patent Application Publication No.2000-183001 also has a disadvantage in that it cannot precisely analyze the color components of RGB since the color components are detected without splitting the reflected light by the color identification sensor. Consequently, the polishing end point cannot be accurately detected.
Moreover, in a method for detecting the polishing end point by using the light of a single wavelength, an erroneous determination often occurs because the polishing end point is detected by referring to data from a single source.
It is an object of the present invention to provide a polishing end point detecting device for a wafer polishing apparatus which can accurately detect a polishing end point.
In order to achieve the above-described object, the present invention provides a polishing end point detecting device for a wafer polishing apparatus, comprising: a light source; a light guide at an illuminating side which conducts light outputted from the light source onto a polishing face of a wafer so as to illuminate the polishing face; a light guide at a light receiving side which conducts the light being reflected on the polishing face of the wafer after having been led from the light guide at the illuminating side onto the polishing face of the wafer; a spectroscope for splitting the light conducted by the light guide at the light receiving side into lights for corresponding wavelengths; a photoelectric converting device for converting the light having been split by the spectroscope into electric signals corresponding with a light intensity of each of the wavelengths, and outputting the converted lights as light intensity signals for the corresponding wavelengths; and an end point determination device for determining a polishing end point in accordance with the light intensity signals for the corresponding wavelengths that have been outputted from the photoelectric converting device.
According to the present invention, illumination light is conducted and reflected light is picked up by using the light guide at the illuminating side and a light guide at the light receiving side; thus light can be more efficiently used and the detecting accuracy improves as compared with a case using a beam splitter. Moreover, the polishing end point detecting device can also prevent the detecting accuracy from being lowered due to a displaced optical alignment. Further, since the reflected light having been picked up is split by the spectroscope, and the polishing end point is detected in accordance with the light intensity distribution for corresponding wavelengths of the split light, the color components of the reflected light can be precisely analyzed, and thus the polishing end point can be accurately detected.
In order to achieve the above-described objects, the present invention provides a polishing end point detecting method for a wafer polishing apparatus, in which a wafer is pressed against a polishing pad and the wafer is polished by sliding the wafer and the polishing pad each other while supplying slurry; wherein white light is applied onto the wafer which is being polished from the light source through a window that is formed on the polishing pad, and a spectrometric analysis is performed to the light that is reflected on the wafer, whereby the polishing end point of the wafer is detected.
According to the present invention, the white light is applied onto a wafer which is being polished, and a spectrometric analysis is performed to the reflected light so as to detect the polishing end point of the wafer. Therefore, more data is available which can be used for detecting the polishing end point as compared with a case for detecting the polishing end point with light of a single wavelength, and hence the polishing end point can be accurately detected.
In order to achieve the above-described objects, the present invention provides the polishing end point detecting method for the wafer polishing apparatus, wherein the spectrometric analysis comprises the following steps: a light intensity spectrum of the reflected light is measured; a ratio between the light intensity spectrum of the reflected light and a light intensity spectrum of the reflected light of a reference sample which has been obtained beforehand is obtained; and the polishing end point is detected based on the obtained ratio.
According to the present invention, the light intensity spectrum of the reflected light is measured, and a ratio is obtained between the light intensity spectrum of the reflected light and the light intensity spectrum of the reflected light from the reference sample that has been obtained beforehand, then the polishing end point is detected based on the ratio. Therefore, the present invention can detect the polishing end point even more accurately than a conventional device and method.
Further, in order to achieve the above-described objects, the present invention provides the polishing end point detecting method for the wafer polishing apparatus, wherein an amount of the reflected light is measured, and brightness of the light source is corrected so that the amount of the reflected light is constant.
According to the present invention, variations in an amount of reflected light due to changes in transmittance of the window with a different surface condition can be corrected, and an amount of reflected light is always maintained constant; thereby, the polishing end point can always be detected accurately.
In order to achieve the above-described objects, the present invention provides the polishing end point detecting method for the wafer polishing apparatus, wherein the light intensity spectrum of the reflected light from the reference sample is corrected in accordance with the brightness of the light source that has been corrected.
According to the present invention, the light intensity spectrum of the reflected light from the reference sample is corrected in accordance with changes of the brightness of the light source; thus the polishing end point can be detected even more accurately than the conventional method and device.
Furthermore, in order to achieve the above-described objects, the present invention provides the polishing end point detecting method for the wafer polishing apparatus, wherein the brightness of the light source is corrected by changing an amount of electricity to be supplied to the light source.
According to the present invention, the brightness of the light source is corrected by changing an amount of electricity to be supplied to the light source.
In order to achieve the above-described objects, the present invention provides the polishing end point detecting method for the wafer polishing apparatus, wherein the brightness of the light source is corrected through the following steps: providing plural light sources with different brightnesses; and selecting one of the light sources to light up.
According to the present invention, plural light sources with different brightnesses are provided, and one of the light sources is selected to light up so as to correct the brightness of the light source.
As described hereinabove, according to the present invention, the reflected light which has been applied on the polishing face of the wafer is split by the spectroscope, and the polishing end point is determined in accordance with the light intensity distribution for corresponding wavelengths of the split lights. Therefore, the color component of the reflected light can be precisely analyzed and the polishing end point can be accurately detected. Moreover, the applied light is conducted and the reflected light is picked up by using the light guide at the illuminating side and the light guide at the light receiving side; thus, the light can be more efficiently used and the detecting accuracy improves as compared with the case using a beam splitter, and at the same time the detecting accuracy is effectively prevented from being lowered due to a displaced optical alignment.
Moreover, according to the present invention, the white light is applied onto a wafer which is being polished, and a spectrometric analysis is performed to the reflected light so as to detect the polishing end point of the wafer. Therefore, more data is available which can be used for detecting the polishing end point as compared with a case for detecting the polishing end point with light of a single wavelength, and hence the polishing end point can be accurately detected.
Furthermore, variations in an amount of reflected light due to changes in transmittance of the window with a different surface condition can be corrected, and an amount of reflected light is always maintained constant; thereby, the polishing end point can always be detected accurately.